Where has me nut post gone then !!

[noggythenog]

If the shaft was thicker on the 98's then wouldnt it require a different nut altogether with a different part number???

[TonyW]

Its more to do with the tolerances  of the nut /shaft interface. I didn't measure the thread pitch but I guess its M18x1.25 (fine thread) which means the shaft size should be between 17.76mm and 17.97mm  this variation allows for worn tools or machinery when cutting the thread. Outside of this the thread SHOULD fail quality inspection.
The nut thread Should be 16.65mm to 16.91mm internal diameter. Again I didn't measure mine but I'm guessing that the mod nuts are cut to nearer the 16.65mm to give better overlap on the shaft thread. (The troughs of the nut thread should be 18-18.3mm)
In this case it looks like the shafts have been cut to the wrong diameter. However it appears that Yamaha feel that with the thicker nut there is enough surface area in contact to keep the nut tight using bearing retainer even if the shaft is down to 17.5mm (bearing retainer is similar to threadlock but has better gap filling properties).
I think that explains it clearly, if not I'll draw a picture to make it easier to understand

[fazersharp]

Pictures please !!
Do we (tony w ) have any theorys as to why yamaha are saying 98s are ok and do not need the nut mod. Are you measuring the shaft including the tops of the thread. Someone on here measured theirs to be 17.5, could it be that the first bikes off the factory line sold like hot cakes and they said oh crap we are gonna need a shed load of parts, which came from extra- different suppliers. So all the 98s are good and some other 99s onwards are not, depending on who supplied the blank shaft that yamaha then cut the thread as if it were a thicker shaft meaning that the threads were not deep enough. And the new nut as you say is cut to fit a 17.5 shaft and it that that is the inportant mod and not the fact that it is 12mm instead of 9mm as the extra 3 mm does not do anything as it sits over the tapered end of the shaft anway. Yam spec loctite 620 which is a very strong thread loc http://www.henkel.co.uk/fullproduct-list...000000IZEY

[TonyW]

Measure at the tips of the thread to get the male thread diameter. Theory: This is simply a quality control balls up. I don't know what manufacturing process Yamaha uses but probably a CNC lathe is used to cut the shaft thread. At some point either a wrong number was progammed in or something else changed. Something as simple as the cutting bit manufacturer changed the overall length of the tool. Possibly they changed the machine used for making the shafts to one with a faster work rate or one the could do multiple operations like milling the splines then cutting the thread. Yamaha obviously know what happened and when but they're unlikely to tell us. I am now curious to know what the internal diameter of the kit nut is if anyone has one. I'll measure the original nut tomorrow when I get home.

[darrsi]

[quote author=TonyW link=topic=9920.msg102967#msg102967 date=1379722854]
Measure at the tips of the thread to get the male thread diameter. Theory: This is simply a quality control balls up. I don't know what manufacturing process Yamaha uses but probably a CNC lathe is used to cut the shaft thread. At some point either a wrong number was progammed in or something else changed. Something as simple as the cutting bit manufacturer changed the overall length of the tool. Possibly they changed the machine used for making the shafts to one with a faster work rate or one the could do multiple operations like milling the splines then cutting the thread. Yamaha obviously know what happened and when but they're unlikely to tell us. I am now curious to know what the internal diameter of the kit nut is?

[fazersharp]

I think that yam do know when it happend thats why they are saying 98s are good
Ive got a new un fitted nut . But on the vernier gauge choice. what do you think of these http://www.screwfix.com/p/forge-steel-ve...iper/38291 or if I can buy cheeper is that just a waste of time as they wont be acurate

[CRH]

I think that yam do know when it happend thats why they are saying 98s are good
Ive got a new un fitted nut . But on vernier gauge. what do you thing of these http://www.screwfix.com/p/forge-steel-ve...iper/38291 or if I can buy cheeper is that just a waste of time as they wont be acurate

....just bt identical to mine!..think i paid £20 from machine mart last year they should be fine?

[TonyW]

Same as mine as well.

[limax2]

This drawing I did a long time ago shows the extra length of thread engaged with the 12mm nut. (Under "Articles" at top of page there is a category for the FZS600 and under that is a lot of the past info from this site about the nut problem).